Crosslinked polyquinoxaline polymers

ABSTRACT

Crosslinked polymers are produced by the reaction of a linear polyquinoxaline containing a pendant furan group with an aromatic olefinic end-capped compound. The polyquinoxaline polymers have an alicyclic endooxy linkage repeated throughout the polymer at the cross-linking sites where the furan end-capped constituent undergoes a Diels-Alder reaction with the aromatic olefinic endcapped crosslinking agent. Subsequently, the alicyclic endooxy linkage may be aromatized by the application of heat to produce a high performance polymer which is suitable for use in severe environments at temperatures up to 400*C.

United Jones et a]. Sept. 9, 1975 CROSSLINKED POLYQUINOXALINE 3,66l,850 5/1972 Stille 260/50 POLYMERS 3,746,687 7/1973 Duffy et a] 260/50 Inventors: Robert J. Jones, Hermosa Beach;

Michael K. ORell, Manhattan Beach, both of Calif.

Assignee: TRW Inc., Redondo Beach, Calif.

Filed: Oct. 31, 1973 Appl. No.: 411,511

References Cited UNITED STATES PATENTS 2/1972 Augl 260/50 4/1972 Augl ct a]. 260/50 Primary Examiner-Lester L. Lee Attorney, Agent, or Firm-Daniel T. Anderson; Alan D. Akers; Willie Krawitz [5 7] ABSTRACT Crosslinked polymers are produced by the reaction of a linear polyquinoxaline containing a pendant furan group with an aromatic olefinic end-capped compound. The polyquinoxaline polymers have an alicyclic endooxy linkage repeated throughout the polymer at the cross-linking sites where the furan end-capped constituent undergoes a Diels-Alder reaction with the aromatic olefinic end-capped crosslinking agent. Sub sequently, the alicyclic endooxy linkage may be aromatized by the application of heat to produce a high performance polymer which :is suitable for use in severe environments at temperatures up to 400C.

2 Claims, No Drawings CROSSLINKED POLYQUINOXALINE POLYIVIERS Theinvention described herein was made in the performance of work under a NASA contractand is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat. 435; 42 U.S.C. 2457).

CROSS-REFERENC To RELATED APPLICATIONS The furan end-capped bisglyoxal monomers used in the preparation of the monomers of thisinvention are disclosed in copending application entitled Polyqui noxalines and Method of Preparation, Ser. No. 411,513, filed Oct. 31, 1973.

BACKGROUND OF THE INVENTION Polyquinoxalines have been prepared by heating slowly a tetramine and a bisglyoxal in an inert atmosphere at about 250C. The resulting polymer produced by this method is more insoluble than polyquinoxalines produced using other methods. When a sol-- vent medium is employed, equimolar amounts of a bisglyoxal and a tetramine are reacted at elevated temperatures under an inert atmospere, and the polymer precipitates from solution.

H N NH HN, NH

Generally,- polyquinoxalines have .been synthesized from bisglyoxal. which had either ahyclr ogen orphe nylene radical end-cap. Polyqui:noxal ines whichhad the hydrogen radical end-cappnthe bis glyoxal exhibited poorer thermal stability but, better ,adhesiye qualities than polyquinoxalines having the phenylene end-cap on the bisglyoxal. v A i Polymer solubility at high linear molecular weights presented another problem for the prior art polyquinoxalines. This is particularly true for the polymer solubility of the polyquinoxalines. However, by proper selectionof monomers having flexible connecting groups between the aromatic units, solubility of polyquinogsalines below about 500C is improved over polyquinoxalines synthesized from monomers having agre'ater-pro portion of aromatic units.

SUMMARY OF THE lNVENTIONj High performance polyquinoxali nes are produced by the in situ aromatization of polyquinoxalines which have been crosslinked through an alicyclic endooxy linkage between the backbone chains.

The linear polyquinoxaline is produced by the reaction of an aromatic tetramine with an, aromatic furan end-capped bisglyoital monomer which is subsequently crosslinked with an aromatic olefihic end-capped compound according to thefollowing reactionz' out Crosslink T T N? VI 0 l O Rn Ru e i as ==C R'-C i I where R is a tetrafunctional aromatic radical and R temperature range of between 200C and 300C will aromati'ze the endooxy coupling in situ to produce a c'rosslinked polymer which has thermal stability upto and R" are difunctional aromatic radicals. The intermediate quinoxaline polymer contains an alicyclic endooxy bridge at the crosslink connection to provide a LDEscRiPTIoN OF THE PREFERRED structure having a low melting point which permits easier processability prior to final cure by aromatization.

EMBODIMENTS I Crosslinke'd polyquinoxalines according to the pres- Final cure of the polymer is accomplished by heating to aromatize the endooxy bridge according to the following reaction: r

ent invention are made by reacting tetramines with his N===aw N N N C C O C N R N C Polyquinoxalines made according to this invention 65 glyoxals which are end-capped with at least one furan exhibit improved resin flow during fabricating steps as a result of the endooxy structure of the crosslink. When the product fabrication has been effected, heat in the radical. The crosslinking is completed by reacting the furan radical with a dienophile, ie, an olefinic endcapped monomer. Reaction of the diolcfin or dienophile with the furan end-caps produces a crosslink between the linear polyquinoxaline chains which is coupled to the linear chains through an alicyclic endooxy linkage. When final fabrication of the polymer'is ready,

heat is applied to the polymer with the result that the structure: H N NH 2 \R /V 2 H H NH wherein R is a tetrafunctional aromatic radical which may be selected from any of:

a see with an equimolar amount of an aromatic bisglyoxal whose structures are illustrated by the following formulas:

R inthe preceeding formulas is a difunctional aromatic radical which is selected from the following:

'CH -C H,-, and -C H R is an optional monofunctional radical in that it mayor may not be present as a substituent onto the furan end-cap, but if present, it is either a hydrogen radical or an alkyl radical having one to four carbon atoms; RC is a monofunctional radical which is selected from the following: -H,

and

and R" may-be either a hydrogen radical or aphenylene: radical. The mount of the nonreactive end-cappec bisglyoxals as illustrated by 'a formula designated 1) can be present in amounts ranging from 0.00 to 0.95 mole fraction,.and the bisglyoxal designated'as formula (2) ranges from 0.05 to 1.00 mole fraction of the bisglyoxal present in the polymer, the total mole fraction of the two bisglyoxal monomers must amount to 1.00.

The polyquinoxaline produced by the reaction of the tetramine and the bisglyoxal monomersis crosslinked by an olefinic end-capped compound having the formula':

5 wherein Z may be either:

The amount; of the diolefin Crosslinking, agent which is used is equal to the number of furan groups present in the glyoxal monomer, that is, one equivalent weight of the olefinic end-capped compound is used for one equivalent weight of the furan end-capped monomer.

Reaction temperatures for the linear polymerization range from room temperature up to approximately 50C with the higher temperatures reducing the reaction time. Crosslinking of the polyquinoxaline resins will occur in the temperature range of from C to approximately 300C. In situ aromatization of the alicyclic endooxy Crosslinking coupling with the linear polymer will occur in the temperature range of from 200C to approximately 300C.

The polymerization reaction to produce polyquinoxaline polymers may be illustrated as follows:

The crosslinking reaction is illustrated ideally as fol- 20 lows:

. cro i Although it is not critical, solvents may be used to reduce the viscosity of the reactants and facilitate mixing and fabrication. Generally, common solvents may be used, e.g., cresol, dimethylformamide, xylene, pyridine,

dimethylsulfoxide, or N-methyl-Lpyrr olidine.

The invention will be more clearly understood by re ferring to the following example. This example illustrates specific embodiments and should not be construe d as limiting the invention.

EXAMPLE Preparation of Furane Containing Polyquinoxaline To a slurry of 0.643 g (3 =millimo1e) of diaminobenzidine in 7 g ofa 1:1 mixture of xylene and m-cr esol was added a mixture of 1.146 g (2.7 rnillimole) of oxybisbenzil and 0.097 g (0.3 rnillimole) of l,4-bis(2-furylglyoxlyl) benzene during a two-minute period. An addi-.

tional 3 g of solvent mixture was added and the reac tion mixture was stirred under nitrogen for 18 hours.

The viscous solution was then slowly added to 500 ml of methanol in a blender. The fiberous yellow solid was collected by filtration, boiled twice with methanol and dried in vacuo at 140C to give 1.65 g of polymer.

The reaction may be illustrated:

CROSSLINKING REACTION I A mixture of 0.557 g of polyquin oxali ne (prepared above) a'nd 0.0.56 g of bis(4-maleimi dophenyl) :methanewas heated toi204C. In 1 hour a gell wasobtained. The solvent was removed from the polymer at reduced pressure and the polymer so isolated was placed in sulfuric acid to assess if crosslink forn lation occurred. The

polymer was observed to swell in the acid butit was not soluble, indicating the formation of crosslinks.

.The reaction may be illustrated:

Cross l inking and efi 9%? v E O CH CH The crosslinked material was found to be insoluble in the original xylene/m-cresol solvent, and also it was insoluble in concentrated sulfuric acid. 30

The following table sets forth the film and adhesive wherein R is a tetrafunctional radical selected from the properties of the polyquinoxaline which was prepared: group consisting of TABLE Polyquinoxaline PQ Product Form Test Property l. m/m* cr0ss- Tensile strength] 15 Ksi/71 linked ,film elongation Apparent softening 600F point Color Light amber Initial Thermo- 515C (958F) oxidative stability 2. Titanium Alloy Lap shear strength 6Al-4V adhesive specimens Linear polymer with I000 psi at R.T.**

l57r m/m Crosslink 700 psi at 600F sites 5% m/m Crosslinked 2800 psi at RT.

1200 psi, at 600F I571 m/m crosslinked 2000 psi at R.T.

1700 psi at 600F "m/m Mole percent olquinoxuline rings in the polymer processing crosslink sites or crosslinks. I

RT room temperature Films prepared in the table were obtained by casting the linear polymer and the crosslinking agent from a 5 @X /50 percent by volume m-cresol xylene solvent mixture employing a 10 percent by weight solids loading.

The solvent was removed under vacuum, when the films were heated at 200C for four hours to effect a and M cure. Verification of the crosslinked formation was shown by the insolubility of the resin film samples by boiling in the m-cresol/xylene solvent for over 72 where X is selected from the group consisting of --O, hours. v CO, S, -SO

We claim:

l. A method for making crosslinked. polyquinoxalines O O comprisingz H SO O, l

A. reacting (i) an aromatic tetraamine having the 2 structure glyoxal selected from the group consisting of linkage sites;

lie ,endooxy linkage.

tially of the structure:

where R; is a difunctional aromatic radical selected attached by alicyclic endooxy linkage at quinoxaline B. heating the polyquinoxaline in I a" temperature range from 200C to 300C to aromatize the alicyc- 2. Acrosslinked polyquinoxaline consisting essen- J V .-g- 11 a where X is selected from the group consisting of -O, s co -so O O 0"" I s1. Q 5 i 4 IQ l u t 2 ill y i. V r-iziizi CH -C H and --C l-l R is an optional mon'ofun'ctional radical selected from the group con I i T sisting of hydrogen radical and alkyl radical having 1 to f- H Ti 4 carbon atoms; R is a monofunctional radical sez e: z 1': lected from the group consisting of H, T] ll l L fffi .J r'- '1 n *1 r" n and Q- l O --O I 2 g J E I n T gO Z --vz uQ alt u u 40 "5' {X I r g-13 --15-,-. z and R is a monofunctional radical selected from the fi Q Q i i group consisting of --H and ll I Q I r L J II where the amount of l) ranges from 0.00 to 0.95 and I I (2) ranges from 0.05 to 1.00 mole fraction of the bisll ll \II ll -U a I 0") glyoxal, the total mole fraction of the aggregate I K amounting to unity; and (iii) one equivalent weight of T 1 an olefinic endcapped compound having the structure: 0:0 am II a I I z I Z-R'-Z 7 1 1 t r 1 where Z 18 selected from the group consisting of T T 1: l a: L a.) K., l, J

for each equivalent weight of furan monomer whereby a polyquinoxaline is formed having a crosslink chain group consisting of wherein R is a tetrafunctional radical selected from the 16 R:" is an optional mon'ofunctiofial radical selected from the group'consisti'ng 'of hydrogen radical and alkyl radicals having l to 4 carbon atoms; R is a monofunc- 5 tional radical selected from the group consisting of where X is selected from the group consisting of O, t

group consisting of -H and i 20 -CH -C: :H ar1d -C=,H R1 is a clifunctiohal radical 7 selected from the group consisting of Y r v a is a mole fraction rangingfiro nf to 0:95 and b a I through g; respectively is a mole fraction ranging from 0.05 to 1.00 wherein the sum of the mole fractions is and R" is a monofunctional radical tsele'c te'dffrom the equal to unity; and is an integer between 2 and 200 

1. A METHOD FOR MAKING CROSSLINKED POLYQUINOXALINES COMPRISING: A. REACTING (I) AN AROMATIC TETRAAMINE HAVING THE STRUCTURE
 2. A CROSSLINKED POLYQUINOXALINE CONSISTING ESSENTIALLY OF THE STRUCTURE: 